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84 SANDVIK, HALL, AND GRIMWOOD [j. s. M. P. E. These measurements have now been made with greater care and better facilities, and the results check our earlier conclusions in that the level of the noise encountered in practice, in general, is higher than the inherent or irreducible level of film noise present upon careful processing, and that it grows very rapidly as the film is run repeatedly through a projector. In view of these facts, it appears that the ground noise as en- countered in motion picture practice can not be lowered materially by decreasing what has been referred to as the inherent film noise. TABLE I Growth of Ground Noise with Successive Stages of Manufacturing and Processing Noise Level in Db. with Material Film Base Film Base Gelatin-Coated Positive Film Positive Film Positive Film Positive Film Positive Film Treatment None Audibility Network -43 Noise Level in Db. without Audibility Network None Fixed, washed, and dried Developed, fixed, washed, and dried Run through printer once, developed, fixed, washed, and dried Run through printer once with sound negative, de- veloped, fixed, washed, and dried Run through sound recorder once, developed, fixed, washed, and dried -40 -37 -37 -37 -35 -39 -37 -36 -32 -32 -33 -29 However, because of the tremendously important bearing which this question has on any sound recording process, it appears worth while to inquire what determines its irreducible limit. Accordingly, measurements were made to determine the actual noise level in the film at each successive stage of manufacture and processing. The results of these measurements are given in Table I. Columns 1 and 2 give the material and its treatment, respectively, while columns 3 and 4 show the noise level of the several materials and treatments, with and without the audibility network, respec- tively.